1. Field of the Invention
The present invention relates to a polarizing plate used in an image display device such as a liquid crystal display device, an organic EL display device or a PDP and particularly to a polarizing plate used in a liquid crystal display device.
2. Description of the Related Art
A polarizing plate used in an image display device (especially, a liquid crystal display device) is produced as follows. For example, after a polyvinyl alcohol (PVA) film is subjected to a dyeing process, a crosslinking process and a stretching process, the film is dried and laminated between protective layers each made of a transparent protective film such as a triacetyl cellulose (TAC) film. In the dyeing process, the polyvinyl alcohol (PVA) film is dyed with dichroic iodine or dichroic dye. In the crosslinking process, the film is crosslinked with boric acid, borax or the like. In the stretching process, the film is stretched uniaxially. (The dyeing, crosslinking and stretching processes need not be executed separately. Some processes may be executed simultaneously. The sequence of the processes is not particularly limited.)
Incidentally, it is preferable that a protective sheet not curled originally is used as each of the protective layers used for protecting the polarizing plate. When a film made of a material such as triacetyl cellulose (TAC) or polycarbonate is used as the protective sheet, generally, the film is however more or less curled because the film is produced by stretching. If the polarizing plate is curled largely, a portion different in optical characteristic such as in-plane light transmittance is produced by stress acting on the polarizing plate when the polarizing plate is bonded to a panel and used. This causes ununiformity of image display. If the polarizing plate is bonded to a liquid crystal cell in the condition that an adhesive surface of the polarizing plate to be bonded to the liquid crystal cell is curled concavely with respect to the liquid crystal cell, voids are held between the polarizing plate and the liquid crystal cell bonded to each other. For this reason, it is impossible to use the polarizing plate.
The aforementioned curl was heretofore suppressed by a method of adjusting the physical condition of the protective sheet (e.g., see Patent Document 1). In recent years, there was however a demand for a bigger size of the polarizing plate than ever. As the area of the polarizing plate increased, the amount of curl at edge sides increased inevitably. With the increase in the amount of curl in the polarizing plate, there arose again the case where the curl of the polarizing plate brought about the problem of lowering of work efficiency and in-plane variation in various kinds of optical characteristic because of the difficulty of bonding the polarizing plate to the panel. Therefore, an important issue is to suppress the curl of the polarizing plate more sufficiently.
[Patent Document 1]
Unexamined Japanese Patent Publication No. 2002-258049